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From Thomas Becker <tobec...@Tivo.com>
Subject Re: [DISCUSS] KIP-138: Change punctuate semantics
Date Tue, 04 Apr 2017 18:53:23 GMT
Yeah I like PuncutationType much better; I just threw Time out there
more as a strawman than an actual suggestion ;) I still think it's
worth considering what this buys us over an additional callback. I
foresee a number of punctuate implementations following this pattern:

public void punctuate(PunctuationType type) {
    switch (type) {
        case EVENT_TIME:
            methodA();
            break;
        case SYSTEM_TIME:
            methodB();
            break;
    }
}

I guess one advantage of this approach is we could add additional
punctuation types later in a backwards compatible way (like event count
as you mentioned).

-Tommy


On Tue, 2017-04-04 at 11:10 -0700, Matthias J. Sax wrote:
> That sounds promising.
>
> I am just wondering if `Time` is the best name. Maybe we want to add
> other non-time based punctuations at some point later. I would
> suggest
>
> enum PunctuationType {
>   EVENT_TIME,
>   SYSTEM_TIME,
> }
>
> or similar. Just to keep the door open -- it's easier to add new
> stuff
> if the name is more generic.
>
>
> -Matthias
>
>
> On 4/4/17 5:30 AM, Thomas Becker wrote:
> >
> > I agree that the framework providing and managing the notion of
> > stream
> > time is valuable and not something we would want to delegate to the
> > tasks. I'm not entirely convinced that a separate callback (option
> > C)
> > is that messy (it could just be a default method with an empty
> > implementation), but if we wanted a single API to handle both
> > cases,
> > how about something like the following?
> >
> > enum Time {
> >    STREAM,
> >    CLOCK
> > }
> >
> > Then on ProcessorContext:
> > context.schedule(Time time, long interval)  // We could allow this
> > to
> > be called once for each value of time to mix approaches.
> >
> > Then the Processor API becomes:
> > punctuate(Time time) // time here denotes which schedule resulted
> > in
> > this call.
> >
> > Thoughts?
> >
> >
> > On Mon, 2017-04-03 at 22:44 -0700, Matthias J. Sax wrote:
> > >
> > > Thanks a lot for the KIP Michal,
> > >
> > > I was thinking about the four options you proposed in more
> > > details
> > > and
> > > this are my thoughts:
> > >
> > > (A) You argue, that users can still "punctuate" on event-time via
> > > process(), but I am not sure if this is possible. Note, that
> > > users
> > > only
> > > get record timestamps via context.timestamp(). Thus, users would
> > > need
> > > to
> > > track the time progress per partition (based on the partitions
> > > they
> > > obverse via context.partition(). (This alone puts a huge burden
> > > on
> > > the
> > > user by itself.) However, users are not notified at startup what
> > > partitions are assigned, and user are not notified when
> > > partitions
> > > get
> > > revoked. Because this information is not available, it's not
> > > possible
> > > to
> > > "manually advance" stream-time, and thus event-time punctuation
> > > within
> > > process() seems not to be possible -- or do you see a way to get
> > > it
> > > done? And even if, it might still be too clumsy to use.
> > >
> > > (B) This does not allow to mix both approaches, thus limiting
> > > what
> > > users
> > > can do.
> > >
> > > (C) This should give all flexibility we need. However, just
> > > adding
> > > one
> > > more method seems to be a solution that is too simple (cf my
> > > comments
> > > below).
> > >
> > > (D) This might be hard to use. Also, I am not sure how a user
> > > could
> > > enable system-time and event-time punctuation in parallel.
> > >
> > >
> > >
> > > Overall options (C) seems to be the most promising approach to
> > > me.
> > > Because I also favor a clean API, we might keep current
> > > punctuate()
> > > as-is, but deprecate it -- so we can remove it at some later
> > > point
> > > when
> > > people use the "new punctuate API".
> > >
> > >
> > > Couple of follow up questions:
> > >
> > > - I am wondering, if we should have two callback methods or just
> > > one
> > > (ie, a unified for system and event time punctuation or one for
> > > each?).
> > >
> > > - If we have one, how can the user figure out, which condition
> > > did
> > > trigger?
> > >
> > > - How would the API look like, for registering different
> > > punctuate
> > > schedules? The "type" must be somehow defined?
> > >
> > > - We might want to add "complex" schedules later on (like,
> > > punctuate
> > > on
> > > every 10 seconds event-time or 60 seconds system-time whatever
> > > comes
> > > first). I don't say we should add this right away, but we might
> > > want
> > > to
> > > define the API in a way, that it allows extensions like this
> > > later
> > > on,
> > > without redesigning the API (ie, the API should be designed
> > > extensible)
> > >
> > > - Did you ever consider count-based punctuation?
> > >
> > >
> > > I understand, that you would like to solve a simple problem, but
> > > we
> > > learned from the past, that just "adding some API" quickly leads
> > > to a
> > > not very well defined API that needs time consuming clean up
> > > later on
> > > via other KIPs. Thus, I would prefer to get a holistic
> > > punctuation
> > > KIP
> > > with this from the beginning on to avoid later painful redesign.
> > >
> > >
> > >
> > > -Matthias
> > >
> > >
> > >
> > > On 4/3/17 11:58 AM, Michal Borowiecki wrote:
> > > >
> > > >
> > > > Thanks Thomas,
> > > >
> > > > I'm also wary of changing the existing semantics of punctuate,
> > > > for
> > > > backward compatibility reasons, although I like the conceptual
> > > > simplicity of that option.
> > > >
> > > > Adding a new method to me feels safer but, in a way, uglier. I
> > > > added
> > > > this to the KIP now as option (C).
> > > >
> > > > The TimestampExtractor mechanism is actually more flexible, as
> > > > it
> > > > allows
> > > > you to return any value, you're not limited to event time or
> > > > system
> > > > time
> > > > (although I don't see an actual use case where you might need
> > > > anything
> > > > else then those two). Hence I also proposed the option to allow
> > > > users
> > > > to, effectively, decide what "stream time" is for them given
> > > > the
> > > > presence or absence of messages, much like they can decide what
> > > > msg
> > > > time
> > > > means for them using the TimestampExtractor. What do you think
> > > > about
> > > > that? This is probably most flexible but also most complicated.
> > > >
> > > > All comments appreciated.
> > > >
> > > > Cheers,
> > > >
> > > > Michal
> > > >
> > > >
> > > > On 03/04/17 19:23, Thomas Becker wrote:
> > > > >
> > > > >
> > > > > Although I fully agree we need a way to trigger periodic
> > > > > processing
> > > > > that is independent from whether and when messages arrive,
> > > > > I'm
> > > > > not sure
> > > > > I like the idea of changing the existing semantics across the
> > > > > board.
> > > > > What if we added an additional callback to Processor that can
> > > > > be
> > > > > scheduled similarly to punctuate() but was always called at
> > > > > fixed, wall
> > > > > clock based intervals? This way you wouldn't have to give up
> > > > > the
> > > > > notion
> > > > > of stream time to be able to do periodic processing.
> > > > >
> > > > > On Mon, 2017-04-03 at 10:34 +0100, Michal Borowiecki wrote:
> > > > > >
> > > > > >
> > > > > > Hi all,
> > > > > >
> > > > > > I have created a draft for KIP-138: Change punctuate
> > > > > > semantics
> > > > > > <https://cwiki.apache.org/confluence/display/KAFKA/KIP-138%
> > > > > > 3A+C
> > > > > > hange+
> > > > > > punctuate+semantics>
> > > > > > .
> > > > > >
> > > > > > Appreciating there can be different views on system-time vs
> > > > > > event-
> > > > > > time
> > > > > > semantics for punctuation depending on use-case and the
> > > > > > importance of
> > > > > > backwards compatibility of any such change, I've left it
> > > > > > quite
> > > > > > open
> > > > > > and
> > > > > > hope to fill in more info as the discussion progresses.
> > > > > >
> > > > > > Thanks,
> > > > > > Michal
> > --
> >
> >
> >     Tommy Becker
> >
> >     Senior Software Engineer
> >
> >     O +1 919.460.4747
> >
> >     tivo.com
> >
> >
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> >
--


    Tommy Becker

    Senior Software Engineer

    O +1 919.460.4747

    tivo.com


________________________________

This email and any attachments may contain confidential and privileged material for the sole
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or agent of TiVo Inc. is authorized to conclude any binding agreement on behalf of TiVo Inc.
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